Well this one has me a little stumped.

Some back story: 2002 Chevy 1500 LM7 Z71. This truck was turbo. Engine and transmission and fresh built no turbo anymore. Just reloaded a factory tune and installed factory injectors. Truck runs great.

This transmission was newly rebuilt with a 2600 stall and on the first test drive, I have no first gear and no forth gear. After a little research I come up with the 1-2 solenoid (solenoid A). Sure enough, I eventually pop a P0751 code. I dropped the pan and pulled the solenoid. It ohm's at 23 which was in range and with a 12V signal you can hear it close and cannot blow air through it. So as far as I can tell the solenoid is working. I checked the input voltage and it has 12V in the plug no matter what gear the truck is in. If I unplug the harness connector to the transmission and put the truck in manual first, it with use first.

What my thoughts are: a bad wire in the loom somewhere, pcm failure, or tuning error.

Anyone hear of this before or have any other ideas?

 

Try turning off the code and see what it does.